In recent years, various types of chemical supply apparatuses have been employed in the production of semiconductor devices. The chemical supply apparatuses supply chemicals, prepared by diluting stock solutions with pure water or by mixing a plurality of stock solutions, to processing units which are used to fabricate semiconductor devices.
If a chemical supplied to the processing units is unstable due to changes in its composition, aggregation of finely divided particles contained in the chemicals, etc., the semiconductor devices may be defective. Accordingly, what is required is a chemical supply apparatus for supplying stable chemicals.
A conventional chemical supply apparatus for supplying cleaning solution and etchant, which is applied to a single wafer type cleaning and etching equipment, is now described with reference to FIG. 1.
Referring to FIG. 1, chemicals are fed to a mixing tank 14 through a flowmeter 12 according to a measured rate. A heater 16 heats up the chemicals fed to the mixing tank 14. A circulating pump 18 circulates the chemicals in the mixing tank 14 so as to mix the chemicals and achieve a uniform temperature distribution. If the temperature and concentration of the chemicals are within a set value, the chemicals are provided to a nozzle (or processing bath). For example, in case of 300 mm wafer, the amount of a chemical used in each chamber is 0.5 l˜1 l/min. Therefore, a chemical tank having a capacity of 45 l can treats 40˜80 wafers even considering their loss.
If the chemical level of the mixing tank 14 falls below a dangerous level, chemical supply is stopped and the mixing tank 14 is refilled with the chemical. The chemical refilling includes the steps of (1) providing a chemical to the mixing tank 14 and (2) heating and mixing the chemical to achieve chemical temperature and concentration needed for a process. In general, the chemical refilling takes about 30˜60 minutes. The conventional chemical supply apparatus 10 cannot provide a chemical to a processing unit during the time required for the chemical refilling (exchanging). Further, only a few nozzles can be provided to one system in the conventional chemical supply apparatus. Thus the conventional chemical supply apparatus needs the same number of supply means as chambers in order to provide nozzles to lots of chambers. In addition, the conventional chemical supply apparatus cannot recycle and reuse a chemical used in the processing unit.